The present invention relates to a method for correcting a conduction defect in a liquid crystal display device and a manufacturing method of the liquid crystal display device using the method, particularly to a method of correcting a conduction defect on a conducting part, which is provided between substrates in a liquid crystal panel.
A liquid crystal display device according to a direct matrix method (direct matrix liquid crystal display) is provided with a pair of substrates. An electrode pattern composed of transparent electrodes such as an ITO is formed on each of the substrates, and an alignment film made of a material such as polyimide is formed thereon so as to cover the electrode pattern. A pair of the substrates are fixed to each other at the circumference with a sealing material, which is made of a material such as an epoxy resin, while surfaces of the substrates, that have the electrode patterns, are opposed to each other and spacers maintain a predetermined gap therebetween. Further, a liquid crystal material is filled into a gap surrounded by a sealing member at the circumference between the substrates.
In the direct matrix liquid crystal display device with such a construction, voltage is applied between the electrode patterns formed on the substrates so as to generate an electric field in a liquid crystal material at a position (cell) where the electrode patterns are opposed to each other. With this arrangement, a polarizing property of the liquid crystal material is controlled so as to display an image.
In the above direct matrix liquid crystal display device, the ends of the electrode pattern are drawn to the ends of the substrates to connect a driver for applying voltage between the electrode patterns, so as to form a terminal part. In some direct matrix liquid crystal display devices, a terminal part is disposed only on one of the substrates to connect terminals together to the driver. In such a direct matrix liquid crystal display device, conducting members made of carbon paste and silver paste are disposed between the substrates so as to form a conducting part, in order to connect the terminal part and the electrode pattern on the substrate having no terminal part thereon.
Referring to FIGS. 8(a) and 8(b), the following explanation describes the construction of a conducting part according to a conventional art. FIG. 8(a) is a plan view showing the construction of the conducting part in accordance with the conventional direct matrix liquid crystal display device. FIG. 8(b) is a sectional view taken along Axe2x80x94A line shown in FIG. 8(a).
The direct matrix liquid crystal display device has a construction in which a scanning electrode terminal 104 and a scanning electrode 110 are brought into electrical conduction via conducting members 106. The scanning electrode terminal 104 is formed on a lower substrate 102 and the scanning electrodes 110 are formed on an upper substrate 108. Further, a large number of the scanning electrodes 110 form an electrode pattern of the upper substrate 108. Here, the conducting members 106 are patterned and formed according to printing method and so on, and conduction is made between the scanning electrode terminal 104 and the scanning electrodes 110 with a one-to-one correspondence.
Moreover, a sealing member 112 is disposed at the circumference of the upper substrate 108 so as to surround the electrode pattern composed of the scanning electrodes 110. Besides, liquid crystal material (not shown) is sealed into an area surrounded by the upper substrate 108, the lower substrate 102, and the sealing member 112. Here, an alignment film, data electrodes forming the lower substrate 102, and a data electrode terminal connected to a data electrode are omitted in FIGS. 8(a) and 8(b).
In the conducting part with such a construction, a conduction defect or a broken wire has hardly occurred between the scanning electrode terminal 104 and the scanning electrodes 110.
However, in the case of the construction in which the conducting part is formed according to the printing method and so on, it has been difficult to meet the needs for a larger display capacity of a liquid crystal display device and a fine pitch of an electrode pattern.
Thus, a construction has been adopted in which fine conducting members are dispersed into a sealing member so as to form a conducting part. Referring to FIGS. 9(a) and 9(b), the following discusses the above construction. FIG. 9(a) is a plan view showing another construction of the conducting part according to a conventional direct matrix liquid crystal display device. FIG. 9(b) is a sectional view taken along line Bxe2x80x94B shown in FIG. 9(a). Those members that have the same functions and are described referring to FIGS. 8(a) and 8(b) are indicated by the same reference numerals and the description thereof is omitted.
In this construction, conducting members 114 are used in place of the conducting members 106 of FIGS. 8(a) and 8(b). Further, the conducting m embers 114 are disposed in the sealing member 112 so as to form a conducting part.
The conducting part is formed as follows: particles serving as the conducting members 114 with conductivity are dispersed into the sealing member 112, and an upper substrate 108 and a lower substrate 102 are bonded to each other via the sealing member 112. Here, when bonding the upper substrate 108 and the lower substrate 102 together, a suitable pressure is applied. This arrangement makes it possible to squeeze and remove a material of the sealing member 112, which is disposed between the conducting members 114, a scanning electrode terminal 104, and a scanning electrode 110. Thus, the conducting members 114, the scanning electrode terminal 104, and the scanning electrode 110 directly come into contact with one another so as to secure conduction.
However, when the conducting part of FIGS. 9(a) and 9(b) is formed according to the above method, a material of the sealing member 112 (hereinafter, referred to as an intermediate sealing member) cannot be sufficiently removed in some of a large number of the conducting parts, so that sufficient conduction may not be achieved.
In this case, the conducting part is formed between the scanning electrode terminal 104 and the scanning electrodes 110. Thus, when a voltage is applied to the scanning electrode terminal 104, the conducting part with insufficient conduction, i.e., the conducting part with a high electrical resistance (hereinafter, referred to as a defective conducting part) may cause a drop in voltage. Hence, on a liquid crystal display composed of the scanning electrodes 110 connected to the defective conducting part, a displayed image becomes less sharp or a display itself becomes unavailable. Hence, irregularity or a defect occurs on a displayed image, causing deterioration in display quality.
The defective conducting part is formed under the influence of smoothness and flexibility on the upper and lower substrates 108 and 102 (hereinafter, simply referred to as substrates), and irregular pressures for bonding the substrates.
Also, particularly when a polymeric material such as plastic and resin is used for the substrates, the foregoing problem is more likely to occur. The polymeric material is generally smaller than a material such as glass in hardness on a surface (surface hardness), and the polymeric material is inferior in smoothness as well.
When glass, is used for the substrates, a pressure applied for bonding the substrates causes deformation, but the pressure is small on a part of the substrates that opposes the conducting member 114. Therefore, a pressure is sufficiently applied to the intermediate sealing member so as to completely remove the intermediate sealing member.
Meanwhile, when plastic is used for the substrates, a pressure applied for bonding the substrates results in large deformation on a part of the substrates that opposes the conducting member 114, so that a pressure cannot be sufficiently applied to the intermediate sealing member. Thus, it is difficult to completely remove the intermediate sealing member. Therefore, the conducting member 114 is still coated with the intermediate sealing member so as to increase a contact resistance (connection resistance).
In response, contact on the conducting part may be corrected by mechanical working (physical working) such as partial application of pressure. However, it is difficult for the mechanical working to correct the contact because the conducting member 114 has a small diameter of about 10 xcexcm and the intermediate member 114 has a thickness which is about one tenth of the diameter (1 xcexcm) of the conducting member 114. Furthermore, in the case of the mechanical working, another problem such as a damage (crack, chip, etc.) may appear.
Meanwhile, unlike the mechanical working, publications such as Japanese Unexamined Patent Publication No. 301722/1990 (Tokukaihei 2-301722, published on Dec. 13, 1990) and Japanese Unexamined Patent Publication No. 245125/1991 (Tokukaihei 3-245125, published on Oct. 31, 1991) disclose methods of performing electrical working on a defect of a electrode formed on a substrate.
However, Tokukaihei 2-301722 discloses a method of correcting a short-circuit defect, in which a short circuit occurs between electrodes to be insulated on the substrate. And then, a current which is sufficiently high to melt an electrode is applied in this method. For this reason, this method is not suitable for solving the foregoing problem. Although this publication takes dc, ac, and pulse waveforms as examples of current to be applied to an electrode but does not discuss any proper conditions for a practical use. Consequently, this method cannot be put into practical use.
Besides, Tokukaihei 3-245125 discloses a method wherein a defective part on a wire is cut in advance by applying a high voltage to an electrode, so as to select a defective product. A break may appear on the defective wire over time. Thus, this method is not suitable for solving the foregoing problem. Further, since this method instantly applies a voltage of about 5 kV, a liquid crystal material may be subjected to electrolysis.
The objective of the present invention is to provide a conduction defect correcting method for a liquid crystal display device and a manufacturing method thereof, that is capable of correcting a conduction defect appearing on a conducting part so as to improve display quality of the liquid crystal display device and a manufacturing yield while preventing a mechanical working, etc. from causing damage on a substrate in the liquid crystal display device, which includes the conducting parts for providing conduction between the substrates.
In order to attain the above objective, the conduction defect correcting method for the liquid crystal display device of the present invention, the device including a pair of substrates having a liquid crystal material therebetween, conductive wires respectively formed on opposing surfaces of the substrates, conducting parts having conducting members with conductivity between the conductive wires, and a sealing member provided around the conducting parts to bond a pair of the substrates together, the method including a step of applying ac voltage to the conducting parts from the conductive wires in the liquid crystal display device.
According to this method, ac voltage is applied from the conductive wires to the conducting parts surrounded by the sealing member while the conducting members with conductivity are sandwiched between the conductive wires formed on the substrates.
In the conducting part, the conductive wires and the conducting members are brought into contact with each other so as to make electrical conduction. However, the sealing member is provided around the conducting part, so that the sealing member may remain between the conductive wires and the conducting parts particularly in a forming process of the sealing member so as to interfere with electrical conduction.
In contrast, according to the foregoing method, when ac voltage is applied from the conductive wires, heat is generated on the conducting part having a conduction defect. The heat is caused by dielectric dissipation in the sealing member disposed between the conductive wires and the sealing member. The sealing member is softened by heating, so that the sealing member may be removed between the conductive wires and the conducting members. Or application of ac voltage from the conductive wires may cause puncture in a thin film of the intermediate sealing member. These effects achieved by application of ac voltage make it possible to improve contact between the conductive wires and the conducting members so as to correct a conduction defect.
As a result, in the liquid crystal display device, it is possible to prevent degradation in display quality resulted from a conduction defect on the conducting part. Also, it is possible to suppress a reduction in yield that is caused by a conduction defect.
With the above method, the conduction defect correcting method for the liquid crystal display device according to the present invention preferably applies the ac voltage to a plurality of the conducting parts in parallel.
According to the above method, when a plurality of the conducting parts are provided, ac voltage is applied to the conducting parts in parallel. This arrangement makes it possible to apply equal voltages to the conducting parts so as to simultaneously correct the conduction defects of the conducting parts. Thus, it is possible to equalize contact resistances on the conducting parts so as to suppress unevenness, etc. on a display image.
Besides, in order to apply ac voltage in parallel, it is only necessary to apply voltage simultaneously to electrode wires on each of the substrates so as to simplify the construction for applying ac voltage.
Consequently, the simple construction makes it possible to improve the display quality of the liquid crystal display device.
With the above method, the conduction defect correcting method for the liquid crystal display device according to the present invention preferably has the following construction: a first electrode and a second electrode are formed respectively on the substrates so as to be opposed to each other via the liquid crystal material, conductive wires formed on one of the substrates act as the first electrode, conductive wires formed on the other substrate act as a first terminal for applying a potential to the first electrode, and the ac voltage is applied between the first terminal and a second terminal for applying a potential to the second electrode.
According to this method, like a direct matrix liquid crystal display device, the ac voltage is applied between the first terminal and the second terminal in the liquid crystal display device, in which the first electrode and the second electrode are opposed to each other via the liquid crystal material, the first terminal and the second terminal are provided for applying a potential respectively to the electrodes, and the conducting parts are formed between the first electrode and the first terminal.
According to the above method, ac voltage is applied between the first terminal and the second terminal so as to apply ac voltage between the first electrode and the first terminal from the second electrode via the liquid crystal material, that is, the conducting parts. Moreover, as the first terminal and the second terminal, it is possible to adopt terminals for connecting a driving circuit which drives the liquid crystal display device of the present invention.
Therefore, the above method can be practiced in a device which is substantially identical to an inspection device used for applying voltage between the first terminals and the second terminals, in a process such as a lighting display inspection in a manufacturing process of a liquid crystal display device, and the method can be practiced in successive steps.
As a result, it is possible to correct a conduction defect while reducing the number of the steps and simplifying the process and facilities by sharing an inspection device, an instrument and so on.
In order to attain the foregoing objective, the manufacturing method of the liquid crystal display device of the present invention, the device including the conductive wires which are formed on the opposing surfaces of a pair of the substrates having the liquid crystal material therebetween and which are electrically connected to each other via the conducting members with electrical conductivity that is disposed into the sealing member to bond a pair of the substrates together, the method including the step of applying ac voltage between the conductive wires after a pair of the substrates are bonded to each other while part of the sealing member that has said conducting member is disposed between the conductive wires.
According to this method, the substrates are bonded to each other while the sealing member having the conducting members dispersed therein are disposed between the conductive wires, so that the conducting members come into contact with the conductive wires. Thus, electrical conduction can be secured between the conductive wires. However, the conducting members have been dispersed in the sealing member, so that the sealing member may remain on a contact with the conductive wires, resulting in a conduction defect.
In contrast, according to the aforementioned method, ac voltage is applied between the conductive wires, so that heat is generated by dielectric dissipation in the sealing member, which provides insulation between the conductive wires, so as to soften the sealing member, or the sealing member is subjected to puncture. Consequently, the contact is improved so was to correct a conduction defect.
Consequently, in the manufacturing method of the liquid crystal display device, it is possible to correct a conduction defect while preventing damage on the substrate that is caused by a mechanical working such as a partial application of pressure for improving contact. Further, this arrangement makes it possible to improve a yield of the liquid crystal display device.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.